This invention relates to methods and apparatus for comparing the condition of an article at different times.
In many industrial applications, it is important to know that the condition of an article after having been subjected to some operation is unchanged. An example is a drill bit or a multihead tool array where the or a drill or other tool might become damaged during a drilling operation and it is important that the damage be discovered and the machine stopped before proceeding to the next operation. The problem is aggravated by the fact that different tools or tool arrays might be used in succession.